This is an ongoing project that i've been working on to see the potential of interactive stereoscopic installations in examining the perceptual process. I use a setup that i've called a Diplopiascope to investigate this. The Diplopiascope has gone through a few changes but basically it is a stereoscopic viewer that allows the viewer to control the images they are being shown through an analog device.

How does it work?

Stereopsis is the perception of depth through an object being seen with both eyes. Due to the horizontal separation of the eyes, two slightly different views of the same scene are shown to each retina. This information, along with several other cues, is used by the brain to calculate depth.

This effect is simulated in the Diplopiascope by presenting stereoscopic films or images to the left and right eyes via projectors or monitors. The viewer is seated and views the images simultaneously through a mirrored viewing device.

I was interested to see what happens when we present different views to each eye at the same time. This is called binocular rivalry. What happens if we show the same scene at different times? What about greatly different viewpoints of the same object? What if the viewer is put in control of what they see through some physical controls?

This tutorial is more a guide to making the viewing apparatus for experimentation than a physiological explanation of stereopsis itself, and it doesn't go into much detail about how to make stereoscopic films as there is already lots of great information about this online.

Here are two videos of the Diplopiascope being used. The designs are slightly different but the idea is the same.

The videos of the drummer used in the installation above were shot with two cameras from a fixed position. The videos were then looped and projected independently. The videos are viewed through a mirrored viewing device, the left eye being shown the footage from the left camera, the right eye the footage from the right. (In actual fact, the videos are inverted horizontally due to being seen through mirrors. To counter this, the videos were inverted horizontally in the projector settings).

Due to the videos being ever so slightly different lengths (about 100 milliseconds), when looped they become increasingly out of synch. Because of this, while the stationary objects in the video (the drum set, wooden frame, cones, walls, etc.) are seen in crisp stereoscopic 3D, the moving objects (the drummer, people, etc.) will be seen in double. This produces a strange effect as the brain switches uncontrollably between which information it perceives, jumping randomly from the left eye to the right dominating perception. What it looks like is difficult to explain, but the moving objects take on a very strange phantom-like presence in the realness of their solid stereoscopic surroundings. While the majority of the field of view remains fixed in pleasant 3D, the figure of the drummer seems to jump in and out of time frames and consciousness itself.

The speed and direction of the videos are controlled by the viewer through an analog device connected to the PCs via arduinos. There are two speakers, one from each PC, and the audio matches the videos and is also controlled by the dials.

The video above shows a slightly different version of the installation. The principle behind the viewing method remains the same, but one difference is the actual videos being show. In the first example, the videos were shot stereoscopically from a fixed position. In this case, the videos were shot using a mobile camera rig (detailed later). The rig is designed so that it can break apart and come together again seamlessly. By filming along two long pathways of shrine gates, I wanted to see what happened if the left camera (left eye) went down one path and the right camera (right eye) down the other. The left and the right pathways in the video are very similar, but not identical. Would our brains be able to compensate for the little differences in the scenes we see? Would we perceive a unified view of one solid pathway, or would it just give us a headache?

Again the speed and direction of the videos are controlled by dials so the viewer can adjust the images they are being shown. By doing this they are able to play around with uniting and rupturing their visual perception.

hi I play also with this idea. but I found a problem. we filming with the 2 camera's parallel I had a problem with aligning. I you look with you eye your eyes make a focal punt. the not parallel. with a stereo picture you can compensate this with an aliging option. but what is an object is comming to you. try to look at your finger with streched arm and move it to you nose. how can I cover this problem using a film?

I am trying to make a telestereoscope. Well, I made a couple but everything is placed by hand and glued--so the effect is a little ragged. How did you adjust your mirrors so get just the right angles. The mechanical part of this is what bothers me. I made one with my daughter where the outside mirrors were quite far apart and when I pointed at her my arm looked like it was about 7 feet long. It was a great effect but I want to use it in a class where the students wouldn't likely be patient. So I want an easy way to make the measurements perfect.

Hi. I used a 90 degree bracket from a hardware store to make the mirrored viewing device. It will never be exactly 90 degrees but this is no problem as by altering the angles and positions of the monitors you can adjust for this. If you are making a hyperscope/ telestereoscope then you will need 4 mirrors in total, right? Try loosely fixing the base and then fine tuning the angles before fixing them permanently. I found that it is best to change the angles by actually looking through the device and moving the mirros until it "fits".

Hi Prakis. By "lag" do you mean the time differences between the two videos? If so, then it is very easy to avoid. Just edit the videos so they are exactly the same lengths and loop them in synch. You could use just one dial to control speed and playback of both videos simultaneously, but it might not be that interesting. If you mean the lag between the physical movement of the dial and the change in the video then there really isn't much of a lag to start with. I messed around with the video compressions and setting to find the ones that worked the smoothest, but this can easily be done in most video editing software.

Thanks for the reply, I am talking about the lag between the real event and the one displayed in the display, normal webcams have a little lag from the real event. If we wave hand before the camera, we can see it happening few milliseconds later. I am wondering how can we completely avoid any lag from the live video to the one on display. This is especially needed if we mount the camera to the second person and look at ourself through the display.

Ah, you mean in the live webcam version in the "Taking it Further" section. Sorry, got you now. Yes, you are right, there is a slight lag present due to the webcams. I used logitech C910 webcams, and the lag was very, very slight, but it was present. I was then applying further effects (like samples from footage recorded 10/20/30 seconds ago) on the PC so this wasn't so much of an issue. But you're right, if you are going for a virtual reality set up then normal video cameras might be a better option. I also tried a set up up to create a kind of out-of-body experience: looking at yourself in real-time 3D. To do this I used the same camcorders as detailed above and linked them up to monitors. There is no noticeable time lag when HDMI cables are used.

"Out of Body experience", that's exactly I was thinking about. Would you like to share your experiences about this experiment ? I still wonder if there is minor lag that is going to kill the complete experience.

I was initially trying to recreate the situation as shown in picture A on this page. The results weren't that exciting however so I started playing around with watching yourself draw from above. I found that a sense of disassociation could be produced if you watch yourself in 3D drawing on paper. I suppose the principle is the same: there is confusion as your vision doesn't match your sense of touch or proprioception.

This is another cool thing from Ramachandran using mirrors. It shows that expensive technology is not always necessary to produce some quite amazing effects.

Truly beautiful! Amazing! This is the kind of inspiration brain-play that I want to see more of, on Instructables, everywhere. Do you have a website or blog? Most preferably, one stream where you post what you've learnt from your experiments, and also articles and videos that you have learnt from?

I would be very interested to see that. I don't know what I can do, but I would love to work with you.

Hi ShutterBugger. Thanks for your comment. I went for a wall-eyed view to make the viewing process itself feel as natural as possible. I find that cross-eyed viewing starts to get quite uncomfortable. Lenses or HUDs would be nice but there is the cost to take into account. Mirrors have a nice simplicity to them.